U.S. patent number 7,608,962 [Application Number 11/868,020] was granted by the patent office on 2009-10-27 for electrical machine and method for setting the field and armature of a permanently excited electrical machine.
This patent grant is currently assigned to Bayerische Motoren Werke Aktiengesellschaft. Invention is credited to Torsten Franke.
United States Patent |
7,608,962 |
Franke |
October 27, 2009 |
Electrical machine and method for setting the field and armature of
a permanently excited electrical machine
Abstract
Electrical machine, having a stator which bears a winding and
having a rotatable rotor, situated at a distance from the stator
via an air gap, which includes at least two coaxial rotor sections
which are rotatable relative to one another, in which each rotor
section bears a system of permanent magnets having polarities which
alternately point outward radially, and having an actuating device
for rotating the rotor sections relative to one another, the
actuating device having a controllable actuator via which the rotor
sections may be aligned with one another with a variable rotary
offset which is independent of a rotational speed of the rotor. In
a method for setting the field and armature of a permanently
energized electrical machine for motor vehicles, the rotational
speed range of the electrical machine is divided into an
armature-setting range, and a freely preselected field suppression
is associated with a particular rotational speed of the rotor.
Inventors: |
Franke; Torsten (Munich,
DE) |
Assignee: |
Bayerische Motoren Werke
Aktiengesellschaft (Munich, DE)
|
Family
ID: |
36293404 |
Appl.
No.: |
11/868,020 |
Filed: |
October 5, 2007 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080036322 A1 |
Feb 14, 2008 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
PCT/EP2006/002109 |
Mar 8, 2006 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Apr 6, 2005 [DE] |
|
|
10 2005 015 657 |
|
Current U.S.
Class: |
310/114;
310/209 |
Current CPC
Class: |
H02K
16/02 (20130101); H02K 2213/06 (20130101) |
Current International
Class: |
H02K
16/00 (20060101) |
Field of
Search: |
;310/112-114,191,209 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2 231 590 |
|
Jan 1974 |
|
DE |
|
3401 163 |
|
Nov 1984 |
|
DE |
|
3800916 |
|
Jul 1989 |
|
DE |
|
42 12 906 |
|
Oct 1993 |
|
DE |
|
1 237 259 |
|
Sep 2002 |
|
EP |
|
2 831 345 |
|
Apr 2003 |
|
FR |
|
2 266 197 |
|
Oct 1993 |
|
GB |
|
2000-201461 |
|
Jul 2000 |
|
JP |
|
Other References
International Search Report dated May 29, 2006 with an English
translation of the pertinent portions (Six (6) pages). cited by
other .
German Search Report dated Jun. 2, 2006 with an English translation
of the pertinent portions (Nine (9) pages). cited by other.
|
Primary Examiner: Le; Dang D
Attorney, Agent or Firm: Crowell & Moring LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of PCT International Application
No. PCT/EP2006/002109, filed Mar. 8, 2006, which claims priority
under 35 U.S.C. .sctn.119 to German Patent Application No. 10 2005
015 657.6, filed Apr. 6, 2005, the entire disclosures of which are
herein expressly incorporated by reference.
Claims
What is claimed is:
1. An electrical machine, comprising: a stator which bears a
winding; a rotatable rotor, situated at a distance from the stator
via an air gap, the rotor including at least two coaxial rotor
sections which are rotatable relative to one another, in which each
rotor section bears a system of permanent magnets having polarities
which point outward radially in alternation; and an actuating
device for rotating the rotor sections relative to one another;
wherein the actuating device has a controllable actuator configured
to align the rotor sections with one another with a variable rotary
offset which is independent of a rotational speed of the rotor; and
wherein the rotor sections are provided on shaft sections of a main
shaft designed as a hollow shaft, in which an inner shaft is
supported in an axially displaceable manner, and the actuator is
designed as a displacement element for axial displacement of the
inner shaft which, in mechanical linkage with a mutually engaged
guide situated on the shafts, provides a freely selectable rotation
and alignment of the rotor sections with respect to one
another.
2. The electrical machine according to claim 1, wherein the first
rotor section is rigidly connected to the main shaft, and the
second rotor section is mounted so as to be rotatable relative to
the main shaft.
3. The electrical machine according to claim 1, wherein the rotor
sections are supported so as to be rotatable relative to the main
shaft, and the inner shaft has a guide groove by means of which a
rotational alignment of the axially displaceable inner shaft with
respect to the outer main shaft may be fixed.
4. The electrical machine according to claim 1, wherein the rotor
has more than two rotor sections which are rotatable relative to
one another.
5. The electrical machine according to claim 4, wherein every other
rotor section is rigidly connected to the other.
6. The electrical machine according to claim 1, wherein the
actuator is designed as a hydraulic piston which may be actuated
via the fluid pressure of a motor vehicle transmission.
7. The electrical machine according to claim 1, wherein the
actuator is designed as an electrical actuator which acts on an
adjustment aid provided on the inner shaft.
8. The electrical machine according to claim 1, wherein the
actuator may be controlled via a centrifugal force regulator which
conforms to the rotational speed of the main shaft of the
rotor.
9. The electrical machine according to claim 1, wherein a guide at
an inner shaft is designed as at least one of axially and helically
extending guide grooves, and a guide at a main shaft is designed as
a guide catch which engages with the guide grooves.
10. The electrical machine according to claim 9, wherein the guide
grooves have different slopes in places.
11. The electrical machine according to claim 9, wherein the guide
grooves are oppositely sloped in places.
12. The electrical machine according to claim 9, wherein the rate
of slope of the guide grooves within a shaft section of the inner
shaft is changeable.
13. The electrical machine according to claims 9, wherein the guide
grooves provided with at least one of different slopes and
progressions overlap one another.
14. The electrical machine according claim 1, wherein the rotor has
spring elements that support the rotor sections relative to one
another, and a preferred state of the rotational position of the
rotor sections may be set by adapting the elastic force of the
spring elements to the rotationally acting magnetic forces which
occur between the rotor sections during operation.
15. The electrical machine according to claim 1, wherein the rotor
sections are designed as intermeshed cups.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an electrical machine having a
stator which bears a winding and having a rotatable rotor, situated
at a distance from the stator by means of an air gap, which is
essentially composed of at least two coaxial rotor sections which
are rotatable relative to one another, in which each rotor section
bears a system of permanent magnets having polarities which
alternately point outward radially, and having an actuating device
for rotating the rotor sections relative to one another.
The present invention further relates to a method for setting the
field and armature of a permanently energized electrical machine,
in particular for motor vehicles, whose rotational speed range is
divided into an armature-setting range and a field-setting range,
having a rotor which has at least two rotor sections which are
rotatable relative to one another, each having a system of
permanent magnets having polarities which alternately point outward
radially.
In automotive manufacturing, in addition to direct current motors
and reluctance motors having an asynchronous design (short-circuit
rotor), electric motors having a synchronous design (claw pole
machine, permanently energized machine) are used. The specific
choice depends on the particular application in which specific
advantages of the particular type of design may be utilized. It is
noted in particular that the electrical machine coupled to the
drive train must cover a wide rotational speed range.
The rotational speed-torque characteristic curve of an electrical
machine is critical for its operating response. A distinction is
usually made between two rotational speed ranges, an
armature-setting range (base rotational speed range) having a
constant maximum torque, and a field-setting range (upper
rotational speed range, also referred to as the field suppression
range for induction machines) ideally having constant maximum
electrical power. The rotational speeds which are possible or
permissible as a function of the particular operating parameters of
the electrical machine are set by the field setting or armature
setting. In the armature setting range, the rotational speed is
usually set by means of the armature setting via the armature
voltage, and for setting higher rotational speeds a field setting
(field suppression) is provided in the field setting range.
In particular in the development of hybrid or electric vehicles, as
well as for generators (i.e., starter generators) of motor
vehicles, good field setting capability is an important criterion
for selecting an electrical machine. Optimal operation in the field
setting range is of the greatest interest for operation of a
generator. For this reason, for the wide rotational speed
distribution of approximately 6000 1/min required in an internal
combustion engine, the claw pole machine or the asynchronous
machine is frequently used, since both have a broad useful field
setting range.
In the claw pole machine, the field is provided directly via the
energizing winding located on the rotor; this type of field setting
is very efficient, and therefore the maximum available machine
power in the field setting range hardly decreases with increasing
rotational speed. However, the field setting of the claw pole
machine is associated with a magnetic circuit--formed from the
closed field lines, i.e., the closed magnetic flux and the
components of the machine (electrical leads, magnets, ferromagnetic
components, generally coated electric sheet steel), including the
bridging of the air gap between the stator and rotor--which is not
well utilized, for which reason the claw pole machine is not
advantageous for higher power.
In the asynchronous machine, the power for the energizing field is
impressed directly via the stator, and the field setting is
provided indirectly via a setting of the phase angle (the angle
between the magnetic and electrical field vectors) of the voltage
impressed in the stator of the motor. The field setting of the
asynchronous machine therefore suffers from significant losses,
causing the maximum available machine power to decrease more or
less strongly (depending on the design) with increasing rotational
speed. This has an unfavorable effect on the operating
response.
In a comparison of the claw pole machine with the asynchronous
machine, the latter is characterized by better utilization of the
magnetic circuit and greater robustness. Therefore, both systems
are competitive for low-power applications. For higher-power
applications, the better utilization of the magnetic circuit is the
deciding factor in favor of using the asynchronous machine.
Permanent asynchronous machines, in contrast, are characterized by
better efficiency, and therefore are likewise favored for these
applications.
For known permanently energized synchronous machines, the field
setting is made externally, i.e., indirectly via the stator. This
is achieved, for example, in the same way as for the asynchronous
machines, indirectly via the phase angle of the voltage impressed
in the stator of the motor.
A disadvantageous effect, however, is that, compared to the
asynchronous machine, an opposing field is generated by the stator
which compensates for the rotor field. The efficiency of the field
setting is therefore relatively low. This causes the maximum
available machine power in the field setting range to drop steeply.
The field setting range is therefore very small, and the usable
rotational speed range generally extends only over the region that
is twice the so-called transition speed (which is frequently equal
to the nominal speed) of the machine. In addition, problems may
arise in the "compensating" or "active" field suppression. If an
error occurs within the engine/generator control system, it is
possible that the field suppression is no longer maintained.
The following two error cases may be described: First, the voltage
induced by the rotor occurs instantaneously at the terminals of the
machine, and is limited only by the load state of an intermediate
circuit capacitor. The energy content of the load is thus delivered
to the intermediate circuit until the intermediate circuit voltage
matches the no-load terminal voltage of the machine. For load
configurations with a driven internal combustion engine or shifting
load (for example, a vehicle in motion), the size of the
intermediate circuit may not be large enough to absorb all of the
energy until voltage equilibrium is established between a converter
and the machine. Second, for a serious error within the engine
control system (converter or terminal short circuit), the continued
energizing of the stator circuit by the rotor causes a
short-circuit torque. This acts as a braking torque on the rotating
rotors and the engine mechanically coupled thereto. Such a response
is undesirable for automotive applications. For a rigid coupling of
the electrical machine to the drive train, this uncontrolled torque
has an influence on the longitudinal dynamics of the vehicle. In
extreme cases, limitation of control over the vehicle is a
possibility.
A brushless motor is known from Japanese patent document JP 2000
201 461 A, including a stator having a winding, and a rotor having
permanent magnets, the rotor being formed from two cylindrical,
coaxially aligned sections, each having a ferromagnetic rotor core.
Each of the two rotor sections is designed as a system of permanent
magnets whose poles point outward in the rotational direction with
alternating polarities. The first rotor section is connected to a
rotational axis in a rotationally fixed manner, and the second
rotor section is mounted so as to be rotatable relative to the
first rotor section.
For changing the rotary offset of the two rotor sections with
respect to one another, a mechanism is provided which acts
independently of the rotational speed of the rotor. The rotating
mechanism is based on a force effect on the second rotor section
which depends on centrifugal force. For this purpose, circular
arc-shaped grooves are provided in the radial direction in the
rotor core in this rotor section which engage with the movable
auxiliary axles. The auxiliary axles are supported by a fixing
plate which is attached to the rotational axis and is provided with
the corresponding slotted holes. On the side of the fixing plate
facing away from the rotor, the ends of the auxiliary axles are
connected to radial circular arc-shaped articulated elements which
are held together by means of a spring system, so that the springs
hold the auxiliary axles in position.
At low rotor rotational speeds the auxiliary axles are held in
their starting position, and at increasingly higher rotational
speeds the auxiliary axles move radially into the slots from the
outside due to centrifugal force and cause rotation of the movable
second rotor section which is coupled to the auxiliary axles and
the springs. Depending on the particular relative position of the
magnetic poles of the two rotor sections, the magnetic flux is
altered in the stator winding of the motor. At low rotational
speeds the identical polarities of the rotor sections are aligned
with one another, so that the flux intensity in the poles of the
stator is at a maximum, and at increasing rotational speeds the
rotation of the movable rotor section increases, resulting in
increasing suppression of the flux. As a result, the motor has a
high torque not only at low rotational speeds, the same as in
conventional motors, but may also be operated with relatively high
torque and at high efficiency at high rotational speeds as
well.
A disadvantage of the known motor is that the rotation of the
movable second rotor section relative to the first rotor section is
coupled to the rotational speed of the rotor shaft. The rotation in
particular is proportional to the rotational speed of the shaft.
The absolute magnitude of the displacement is fixedly specified by
the spring mechanism and cannot be changed without great effort.
The possibilities for suppressing the flux or the field setting are
therefore relatively inflexible. In particular, the possibilities
for achieving a field suppression characteristic of the machine
along a given characteristic curve are limited.
A permanently energized electrical machine is known from German
patent documents DE 34 01 163 C2 and DE 38 00 916 A1 in which the
rotor includes a system of permanent magnets, each magnet being
enclosed by a lamellar soft iron casing alternately composed of
magnetically conductive and nonconductive layers. The magnetic
field which acts in the air gap between the rotor and the stator
extends in the rotor through the lamellar soft iron system and
forms a magnetic circuit. The field setting may be achieved, for
example, via the armature current, but with the disadvantages
described above. For applications in which it is not necessary to
rapidly alter the magnetic field, DE 34 01 163 C2 proposes a
displaceable soft iron element in the rotor, which when displaced
causes the magnetic circuit to increase in size, thereby
suppressing the air gap field. The magnetic field may be actuated
in this manner.
It is disadvantageous that the displaceable soft iron actuating
element has a relatively complex structure, and is appropriate only
for certain designs. In particular for a rotating machine,
complicated design measures are necessary for installing and
actuating the displaceable actuating elements. In addition, the
possibilities for field suppression by the soft iron actuating
element are limited. In particular for electrical machines rotating
at high rotational speeds with the widest possible field setting
region, as required in the automotive field, the known system is
thus unsuitable.
An object of the present invention, therefore, is to provide an
electrical machine having the design of a permanently energized
synchronous machine which combines a wide field setting or field
suppression range with a high field setting efficiency and improved
field suppression variability, and ensures a higher level of
operational reliability.
This and other objects and advantages are achieved by exemplary
embodiments of the electrical machine in accordance with the
present invention, in which an actuating device has a controllable
actuator via which the rotor sections may be aligned with one
another with a variable rotary offset which is independent of a
rotational speed of the rotor.
According to the invention, a permanently energized machine is
provided in which the field setting in the rotor itself is possible
as a result of an externally actuatable rotary offset of two or
more mutually rotatable rotor sections. The invention is also
applicable to direct current machines as well as induction machines
having any given number of winding phases and poles. In addition,
the interconnected circuitry of individual coils (stator windings)
has no effect on the function according to the invention. For the
functioning of the electrical machine according to the invention,
it is irrelevant whether the machine is designed as an internal
rotor, external rotor, or disk rotor motor. The magnetic return of
the rotor circuit likewise corresponds to the conventional
machines. Furthermore, the step size of the stator winding is not
critical for the function. The principle may be applied to hoop
windings, chorded windings, concentrated windings, etc. In
particular, the field setting in the rotor is not coupled to the
rotational speed of the rotor.
The rotary offset of the rotor sections may be freely adjusted via
the actuating device; i.e., the rotary offset, in the field setting
range as well, does not necessarily change (proportionately) with
the rotational speed of the machine, so that fine adjustment of a
specified field suppression characteristic is possible over the
entire rotational speed range of the electrical machine. The
instantaneous torque is used as a parameter for the instantaneous
rotary offset, although the change in rotary offset as a function
of rotational speed may be any given specifiable function which is
achieved via a corresponding control of the actuating device and
the actuator.
According to the invention, use is made of the fact that the
voltage induced by the rotor in the stator depends not on the
maximum induction of the machine, but, rather, on the total
induction acting on the winding of the stator. Thus, if a conductor
loop (referred to below as a coil) is moved by two equally strong
but opposing magnetic fluxes (which may be generated, for example,
by two permanent magnets of opposite polarity), the resulting
measurable voltage in the coils is zero (superposition principle).
Thus, with regard to the induced voltage, it is not important
whether the fields cancel one another at each location, or whether
in places fields which are different from zero exist which
ultimately cancel one another entirely. To prevent induction of a
voltage in the coil, it is necessary only for the integral of the
time-variable flux over the coil cross section to be zero.
For the electrical machine according to the invention, the
permanent magnets of the rotor are mounted on at least two rotor
sections which are rotatable relative to one another. The resulting
field is altered by rotation of the rotor sections. In particular,
this allows the field suppression to be regulated. The known
disadvantages of the conventional permanently energized synchronous
machines with regard to the field setting range and control of the
torque for serious errors in the control system are avoided. The
machine according to the invention thus combines the respective
advantages of the electrically energized machines (e.g., claw pole
machine, asynchronous machine) with regard to the field setting
capability and utilization of the magnetic circuit with the
advantages of the permanently energized machines with regard to
their relatively simple and economical design and high efficiency.
Compared to the rigid coupling of the rotary offset of the rotor
sections to the machine rotational speed, the free field setting in
the rotor allows more flexible options for operating the electrical
machine.
In detail, the following advantages are realized: The field setting
range may be extended much more widely over the rotational speed.
The field suppression is achieved without losses, since it need not
be impressed via the stator. No impairment of the phase angle is
associated with the field setting, resulting in lower reactive
power requirements for the machine. The control of the machine no
longer need be designed for the reactive power requirements for the
field setting, but, rather, only for the maximum actual power
requirements. This results in advantages with regard to
installation space and costs. In the case of generator operation,
the type of field setting according to the invention ensures
simpler operation with constant machine voltage that is independent
of the rotational speed. The machine is therefore particularly
suited for use in vehicles in which a virtually constant feed from
the generator to the vehicle electrical system is required over a
wide rotational speed range of the internal combustion engine.
Machines which are well controllable and free of stop torque may be
realized without limitations with regard to efficiency and maximum
achievable torque.
When the machine is in no-load mode the field may be set to zero,
thus allowing the machine to operate at any given rotational speed
with essentially no losses. In the event of control errors the
excitation may be reduced to zero in a short time (milliseconds),
thus causing the torque applied by the machine to become zero as
well. The machine according to the invention is therefore
particularly suited for a rigid coupling to the drive train. The
undesired short-circuit torque and its effect on the stability of
the vehicle is avoided by use of the system according to the
invention. It is not necessary for the excitation field to be
generated via electrical paths, and in contrast to electrically
energized machines no excitation power must be provided. The
outlays for the excitation (power supply and circuitry for
providing the excitation power) are lower, and the reactive power
requirement is lower. This results in a more favorable load
characteristic curve (better "cos .phi."). The efficiency as well
as the achievable power density are also higher. The utilization of
the magnetic circuit is greater, and the achievable efficiency and
power density are higher. The weight and volume are lower than for
other electrical machines of the same functionality and power. Due
to the optimized operation, the costs for a feeding converter are
lower than for other electrical machines of the same functionality
and power.
According to one exemplary embodiment of the invention, the rotor
sections are provided on shaft sections of a main shaft designed as
a hollow shaft, in which an inner shaft is supported in an axially
displaceable manner. The actuator is designed as a displacement
element for axial displacement of the inner shaft which, in
mechanical linkage with the mutually engaged guide situated on the
shafts, provides a freely selectable rotation and alignment of the
rotor sections with respect to one another.
For simplicity of illustration, the following description relates
to two rotor sections which are movable relative to one another,
but correspondingly applies for a plurality of sections which are
movable relative to one another.
According to the invention, the adjustment of the two segments
relative to one another is performed in such a way that, for
example, one rotor section is rigidly connected to the main shaft,
and the other section is mounted so as to be rotatable relative to
the main shaft. The inner shaft is positioned in the axial
direction by means of a suitable adjustment aid, such as a
mechanical guide prong or a hydraulically actuated piston. The
positioning is then adjusted by a controlled electrical actuator,
for example, or by means of the fluid pressure of a vehicle
transmission. Besides these very flexible adjustment options which
are independent of the rotational speed, actuation is also possible
via a centrifugal force regulator, by means of which relative
adjustment of the rotor sections directly conforms to the
rotational speed of the rotor or the main shaft, and outside
intervention is unnecessary.
The inner shaft is provided in places with guide grooves in which
matching guide elements or guide catches of the outer shaft engage.
The guide grooves in the sections for the rotor section which is
rigidly connected to the shaft and for the rotor section which is
connected to the shaft in a rotational manner may have different
slopes. The guide grooves of one of the two sections may have an
axially extending design, and the guide grooves of the other
section may have a helically extending design.
According to another exemplary embodiment of the invention, both
sections have opposing slopes. In this configuration the changes in
rotational speed which occur during adjustment of the rotor
sections cancel one another, resulting in response of the overall
system which is advantageous from an energy and control
standpoint.
According to another exemplary embodiment of the invention, both
rotor sections are supported so as to be rotatable relative to the
main shaft, and the guide grooves of the axially displaceable shaft
have a third section which fixes a rotational alignment of the
axially displaceable shaft with respect to the main shaft. In
conjunction with the opposing slopes for the two rotor sections,
the torques to be applied for adjusting the rotor sections also
cancel one another relative to the main shaft, thus further
improving the control response of the system.
According to another exemplary embodiment of the invention, the
slope of the guide grooves is not constant within a section,
thereby optimizing, for example, the force necessary for the
adjustment and the setting range from an energy and control
standpoint. In particular, the slope may decrease in a specific
ratio with increasing offset of the rotor sections relative to one
another. The progression of the slope is provided depending on the
design of the machine and corresponding to the available torques in
the rotational speed range. As a result of the variable slope, the
force required for the adjustment may be minimized for the entire
working region of the electrical machine.
According to another exemplary embodiment of the invention, the
(two) differently configured guide grooves overlap one another. It
is important that the non-intersected length of the guide grooves
is sufficiently greater than the width of the guide grooves in
order to avoid jamming of the guide elements (guide catches) or
replacement of the guide track. A particularly compact system for
the adjustment is achieved by overlapping the guide grooves.
According to another exemplary embodiment of the invention, the
(two) rotor sections are mutually supported by springs in such a
way that compensation is made for the rotational forces which
result from the magnetic field lines formed by switching of the
stator circuit between the (two) rotor sections. In this manner the
rotor sections may be adjusted with respect to one another with a
minimal outlay of force and energy.
The force of the supporting springs may be dimensioned to be
sufficiently less than the rotationally acting magnetic forces
which result between the rotor sections. The relative position of
the rotor sections therefore has a preferred state at maximum field
suppression, and in the absence of control the machine
automatically deenergizes. As a result, the machine is no longer
able to apply an appreciable torque in the event of malfunction.
The force of the supporting springs may also be dimensioned to be
sufficiently greater than the rotationally acting magnetic forces
which result between the rotor sections. The relative position of
the rotor sections therefore has a preferred state at minimum field
suppression, and in the absence of control the machine
automatically assumes the state of maximum excitation. As a result,
the machine is able to apply its maximum torque in the event of
malfunction. The force of the springs may also be dimensioned in
such a way that an average deflection of the two rotor sections,
and thus an average field suppression, is established. Lastly, it
is also possible to adjust the preferred position via springs which
act axially on the axially displaceable shaft. Here as well, the
described working points may be defined as preferred positions.
According to another exemplary embodiment of the invention, the
stator is divided into more than two sections. In particular, the
following two variants may be advantageously implemented:
The individual sections may be adjusted relative to one another
with different offsets. First, the field suppression characteristic
of the machine may be fixed on a specific characteristic curve in a
particularly effective manner. Second, a "skewing" of the rotor may
be varied in order to adapt stop torque and torque ripple to a
specific working point of the machine. It is thus possible, for
example, to provide a high stop torque for a stationary rotor in
order to achieve, for example, a braking or clutch function for a
currentless machine (the offset of the magnets, i.e., the skew of
the rotor, is zero). The stop torque is reduced and canceled by the
increasing offset of the magnets/increasing skewing of the rotor,
thereby releasing the brake or clutch. This method may also be used
to improve the control response of the machine for small torques
without impairing the maximum torque of the machine as the result
of a fixed skewing.
It is also possible to make a rigid mechanical interconnection with
every other section, resulting in two rotor parts which are
intermeshed in a comb-like manner. With a sufficiently fine
division of the rotor, offsetting of the rotor sections suppresses
not only the entire field which acts on the stator coils, but also
the locally acting field as the result of disproportionately
increasing edge effects (termination of flux between the magnets
already in the air gap). In this manner the core losses, i.e., the
additional energy outlay for the magnetic field for bridging the
air gap between the stator and rotor in the form of increased
excitation current, magnetic reversal, and turbulent flow losses,
are further reduced in the stator.
According to another exemplary embodiment of the invention, the
rotor sections are designed as intermeshed cups. The inner rotor
section has a magnetic return, whereas the magnetic return is
avoided for the outer rotor section. The outer rotor section may be
designed as a self-supporting magnetic cup with alternating
magnetization. To realize the return-free design, nonmagnetic
materials, for example plastics or aluminum, may be used as
supports for the individual permanent magnets. When magnetic
support materials are used, dimensioning is possible which causes
saturation of any magnetic short circuits which may occur. For this
purpose, suitable materials or dimensioning guidelines for
saturating magnetic bars are known as such from the design of
electrical machines. The cup design according to the invention
results in a localized compensation of the magnetic field, and
therefore has the advantage of a further reduction of the core
losses in the field setting range. In principle, a cup design
having more than two intermeshing rotor sections is also
possible.
The known methods for setting the field and armature of permanently
energized electrical machines have the disadvantages described
above.
A further object of the present invention, therefore, is to provide
a method in which the field setting of a permanently energized
synchronous machine is more efficient.
This object is achieved in accordance with the present invention by
a method for setting the field and armature of a permanently
energized electrical machine for motor vehicles having a rotational
speed range divided into an armature-setting range and a
field-setting range, by varying a rotary offset of the rotor
sections via controllable actuator in such a way that a freely
preselected field suppression is associated with a particular
rotational speed of the rotor.
As a result of the freely variable field setting or field
suppression in the rotor itself, more efficient and reliable
operation of the permanently energized synchronous machine is
achieved in a wide rotational speed range. By means of fine
adjustment of the rotary offset, in operation the machine conserves
energy with low power losses.
When the machine is operated in the armature setting range, the
rotor sections may have in-phase alignment; i.e., the polarities of
adjacent or oppositely situated magnets are identical, and the
rotary offset relative to one another is zero. The machine may thus
be operated with maximum excitation. In the field setting range,
the rotor sections are rotated relative to one another so that the
magnets are mutually offset and the polarities overlap. The
resulting field is thus suppressed, and the voltage induced in the
stator is correspondingly smaller. The machine may thus be operated
above the so-called transition speed in the same manner as for
externally impressed field suppression at rotational speeds, and
the available torque is correspondingly reduced.
For a shift of the (two) rotor sections by exactly one pole
division (out-of-phase alignment), the resulting field is zero, as
well as the induced voltage resulting in the stator and the torque
applied by the electrical machine. Uncontrolled torque may thus be
avoided in the event of a serious control error.
Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings show the following:
FIG. 1 shows a simplified illustration of an electrical machine
having two rotor sections which are rotatable relative to one
another, in a sectional side view;
FIG. 2a shows a schematic illustration of a rotational alignment of
the two rotor sections at maximum excitation, in a sectional side
view;
FIG. 2b shows a schematic illustration of a rotational alignment of
the two rotor sections at maximum field suppression;
FIG. 3a shows a schematic illustration of a rotational alignment of
a rotor having more than two rotor sections, at maximum
excitation;
FIG. 3b shows a schematic illustration of a rotational alignment of
the more than two rotor sections, at the resulting maximum field
suppression;
FIG. 3c shows a schematic illustration of an alternative rotational
alignment of the more than two rotor sections, at the resulting
maximum field suppression;
FIG. 4 shows a simplified illustration of an electrical machine
having two intermeshing rotor sections which are rotatable relative
to one another, in a sectional side view;
FIG. 5a shows a simplified illustration of a rotational alignment
of the intermeshing rotor sections at maximum excitation, in a
sectional front view; and
FIG. 5b shows a simplified illustration of a rotational alignment
of the intermeshing rotor sections at maximum field
suppression.
DETAILED DESCRIPTION OF THE DRAWINGS
An electrical machine essentially includes a stator 1 and a rotor
2, which is divided into multiple rotor sections 3a-n which are
rotatable relative to one another.
The electrical machine is designed as a permanently energized
synchronous machine, for example in an internal pole (internal
rotor machine) design. The structure and mode of functioning of
such permanently energized synchronous machines are known in
principle. Therefore, a detailed description is provided only for
the rotor 2 according to the invention.
FIG. 1 shows the rotor 2 having two adjacently situated rotor
sections 3a and 3b. The rotor 2 is situated at a distance from the
stator 1 by means of an air gap, and is rotatably supported on a
main shaft 6. The stator 1 is provided with coils and electric
steel sheets in a known manner. The rotor sections 3a, 3b are
designed as magnet wheels, each bearing a system of permanent
magnets 11, the magnetic north pole 12 and south pole 13
alternately pointing outward (FIGS. 2a and 2b). The main shaft 6 is
designed as a hollow shaft into which an inner shaft 8 projects.
The shaft 8 is axially displaceable with respect to the shaft 6. A
guide pin 9 on the main shaft 6 and a borehole 10 in the inner
shaft 8 act as a guiding aid 7. An actuating device 16 is provided
for adjusting the rotor sections 3a, 3b or 3a-n relative to one
another.
The actuating device 16 has an actuator (not illustrated), for
example a controllable electrical actuator, for axial displacement
of the shaft 8. The actuator causes displacement of the shaft 8
along a displacement path which may be preselected by means of a
control unit (not illustrated). The rotor sections 3a and 3b are
provided on shaft sections 14, 15 of the main shaft 6 so as to be
rotatable relative to one another. Provided on the shaft sections
14, 15 are guide elements/guide catches 5a, 5b which engage with
helically extending guide grooves 4a, 4b on the inner shaft 8. An
axial displacement of the inner shaft 8 occurs via the guide
grooves 4a, 4b, and the guide catches 5a, 5b cause the rotor
sections 3a, 3b to rotate relative to one another. Any given rotary
offset of the poles 12, 13 of the rotor sections 3a, 3b may be set
by means of the axial displacement of the inner shaft 8. In
addition, springs (not illustrated) are advantageously provided
between the rotor sections 3a, 3b which establish a preferred
position of the rotor sections 3a, 3b.
A further embodiment of the rotor 2 is illustrated in FIGS. 4 and
5. The rotor sections 3a, 3b are provided as intermeshed cups
(similarly as for FIG. 1, the bearing, force-transmitting elements,
and springs between the rotor sections are not illustrated). The
outer rotor section 3a is designed as a self-supporting cup without
magnetic return. At its inner periphery the inner rotor section 3b
has a magnetic return 17. In other respects the mode of functioning
corresponds to that of adjacently positioned rotor sections.
One method for setting the field and armature of a permanently
energized electrical machine is based essentially on a rotational
alignment of magnetic poles 12, 13 of rotor sections 3a-n, provided
so as to be rotatable relative to one another, of a rotor 2 of the
machine.
The method for the above-described electrical machine according to
the invention is explained below for the case of an electric
motor/generator, having a wide rotational speed range, coupled to
the drive train of a motor vehicle.
The setting of the field or armature along a torque/rotational
speed characteristic curve is provided according to the invention
by varying the rotary offset between the rotor sections 3a, 3b
(rotor having two rotor sections). In the base rotational speed
range (armature setting range) the machine is to be operated at
maximum excitation. The increase in electrical power at maximum
drive torque (nominal torque) is approximately linear. In this
regard, the rotor sections 3a, 3b have in-phase alignment; i.e.,
the polarities of adjacent magnets 11 are identical (the north pole
12 is adjacent to north pole 12, and the south pole 13 is adjacent
to south pole 13), and the rotary offset relative to one another is
zero (FIG. 2a). In order to allow operation of the machine at
rotational speeds above the armature setting range, i.e., in the
field setting range (field suppression range), suppression of the
magnetic air gap field (field setting/field suppression), i.e., a
reduction in the excitation, is necessary. The electrical power
remains approximately at a maximum as the drive torque decreases.
For this purpose, the two rotor sections 3a, 3b are rotated
relative to one another so that the magnets are mutually offset.
The resulting field is smaller for reduced voltage induction in the
stator 1. A maximum field suppression results for out-of-phase
alignment (the north pole 12 is adjacent to the south pole 13) of
the rotor sections 3a+b (FIG. 2b). The field suppression or field
setting may be varied by means of a rotary offset between the
in-phase and the out-of-phase alignments.
For a rotor division having more than two rotor sections (FIGS.
3a-c), the individual rotor sections 3a-n are aligned for maximum
excitation without rotary offset. For the field setting, the rotor
sections 3a-n may be aligned relative to one another with different
rotary offsets. Maximum field suppression results from an
alternating alignment (north pole-south pole-north pole . . . )
(FIG. 3b), or from an increasing offset (north pole-north pole with
rotary offset-south pole) of the individual rotor sections 3a-n
(FIG. 3c). By means of a given rotary offset for each individual
rotor section 3a-n it is possible to achieve a specific field
suppression characteristic curve.
In the case of a cup configuration as illustrated in FIG. 4 or 5,
the magnetic poles 12 or 13 of the outer rotor section 3a and of
the inner rotor section 3b are oppositely situated. At maximum
excitation (armature setting range), the same polarities are
situated opposite one another (FIG. 5a). For a rotary offset, the
oppositely situated poles increasingly overlap (field setting
range) until the opposing polarities are opposite one another (FIG.
5b). This setting in turn produces a maximum field suppression.
The foregoing disclosure has been set forth merely to illustrate
the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
* * * * *